"Castro's prime speaking spot is sure to stoke speculation about his political future, since Obama's keynote address in 2004 helped launch his national political career. As is tradition, also speaking that night will be the First Lady, Michelle Obama. ...

"Castro's Mexican-American heritage and his political skills have put him on the radar as someone who could fill the position of his party's Latino standard-bearer at a time when Latino voters are gaining more and more political influence."

Hinojosa spoke to Henry Flores, a political scientist and dean of the Graduate School at St. Mary's University in San Antonio, who said Castro is a part of a third generation of Latino politicians who "are well-educated, [and] can make policy and debate with the best of the folks around the nation."

Castro and his twin brother both graduated from Stanford. Castro graduated from Harvard Law in 2000. By 2001 at age 26, he had become the youngest councilman in San Antonio and by 2009, he was the youngest mayor of a major American city. Last year, he won reelection with 82 percent of the vote.

In a 2010 New York Times Magazine profile, Castro was called the "post-Hispanic Hispanic" politician because his ideology is complex and sometimes parts ways with many of older Chicanos — like his mother — who were crucial in the civil rights struggle of Mexican Americans. The Times reports, for example, that on the question of the Alamo, Castro doesn't have the same distaste his mother does. They go on:

"A Democrat, Castro is a pragmatist, sometimes unpredictably so. He supports free trade, including the North American Free Trade Agreement, advocates an energy policy that includes fossil fuels, believes in balanced budgets and refers to David Souter as his ideal Supreme Court justice. Like a large plurality of his fellow San Antonians, Castro is a Roman Catholic, but he was the first San Antonio mayor to be grand marshal when he marched in the annual gay rights parade, and he is pro-choice. "We disagree on this, the pope and I," he says with a smile."

Castro released a video today about the keynote address.

"Being the keynote speaker at the convention this year is an honor I don't take lightly," Castro said. "I know I've got some big shoes to fill."

While Castro will be the first Latino keynote speaker at the DNC, NBC Latino notes that in 1984 Katharine Davalos Ortega, who was U.S. Treasurer, gave the keynote address at the Republican National Convention.